Computer devices, such as hard magnetic disk drives have long been used in computer systems for mass storage purposes and are typically the main storage facility having fast random access to stored data. One disadvantage of the hard disk drive is that the disks are fixed in the drive and can not be easily transported to other locations. In the computer environment, it is desirable to insert and remove hard disk drives from their respective computer bus attachments such as a SCSI bus connection. However, when removing or inserting a disk drive onto a computer bus, care must be taken not cause electrical transient signals which may damage other connected components which may otherwise experience a processing failure. It is further advantageous to be able to insert or remove connected devices while the connected computer is active and powered up processing various tasks. Thus, various means have been employed to disconnect (hot removal) and reconnect (hot insertion) peripheral devices from or to data buses connected to and communicating data to and from connected powered up host computer systems.
In Bartol, U.S. Pat. No. 5,210,855, devices to be hot inserted or hot removed are connected through connecting pins mechanically arranged to ensure that connections are made in a particular order, such as ground lines, then power lines, then data lines. These mechanical pin arrangements are subject to failure based upon the;direction of insertion, and do not provide the accuracy and reliability of electrically controlled connections and disconnections.
In Losi, U.S. Pat. No. 5,157,771, an apparatus is disclosed for hot removal or hot insertion of system components, the apparatus including electronic switching means and line biasing circuitry for deenergizing or energizing line switches to reduce the amount of noise introduced. However, noise may still be induced and not completely eliminated.
In Mutoh, U.S. Pat. No. 5,247,619 a system is disclosed wherein circuits boards may be inserted or removed while the system is in operation. As a component is added or removed, the device control circuitry sends a signal to the bus controller requesting that all devices connected to the bus stop sending signals along the bus until the insertion or removal is complete and the bus is again stable. This system disadvantageously requires special signaling to and processing by the other connected devices to essentially ignore the bus conditions during insertion and removal rather than eliminating the transients in the first instance.
In Herrig, U.S. Pat. No. 4,835,737 a system is disclosed for hot insertion and hot removal by the suspension of a clocking signal on the bus. This method does not eliminate the generation of transients, but rather disables connected devices.
The above references, Bartol, Losi, Mutoh and Herrig do not specifically relate to a SCSI bus and the problem of disk drive insertion and removal thereon. These prior arrangements may cause transient on the SCSI lines to occur because the bus lines are not completely isolated during hot insertion or hot removal.
Blackborow, U.S. Pat. No. 5,210,855 relates to isolation of the SCSI bus during hot insertion and hot removal of connected disk drives. Blackborow, discloses a SCSI bus base unit including an interface circuit and a disk drive module. The base unit connects to the SCSI bus through to an adaptor which in turn connects the SCSI bus to a host computer. The system uses a special control status bus which connects between the base unit and the disk module. The base unit includes a SCSI interface circuit and a microcontroller CPU. Blackborow shows a microprocessor controlled interface using special control lines. Significantly, the SCSI bus to the host computer is not completely isolated from transients caused by the insertion or removal of a disk module by virtue of the direct SCSI bus connection between the disk drive module and host computer. The system in Blackborow disadvantageously teaches the direct SCSI bus connection between the host computer and the hot inserted or hot removed disk drive thereby subjecting the host computer and other external disk drives to transients caused by the hot insertion and hot removal of the disk drive module.
Prior computer bus isolation devices disclose the use pin arrangements, special control lines and or switching mechanisms all used to minimize the effect of voltage transients produced by the hot insertion or hot removal of peripheral devices. Consequently, the prior computer bus isolation devices do not eliminate voltage transient during hot insertion or hot removal, but rather attempt to minimize the strength of those transients or to minimize the effect caused by those transients subjecting the connected host computer and the connected devices to transient voltage signals, rather than assuredly completely eliminating the voltage transients. These and other disadvantages are solved and reduced by the present invention.